Nontamperable and noninterchangeable plug fuse



E. H. TAYLOR Feb. 14, 1939.

NONTAMPERABLE AND NONINTEJRCHANGEABLE PLUG FUSE Filed Sept. 2l, 1935 M w al1-1l.. 8 6 M .1\\ QL K Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE N ONTAMPERABLE AND NONIN TERCHAN GE- ABLE PLUG FUSE Application September 21, 1935, Serial No. 41,559

21 Claims.

This invention relates to combined non-tamperable and non-exchangeable plug type fuses.

An electric fuse is intended primarily to protect the circuit with which it is associated against ,damage due toy overloading thereof. A circuit which is over-fused by afuse having a greater current carrying capacity than the safe capacity of the circuit or has the terminals of the fuse receptacle connected by metal having high current conducting capacity is not adequately protected.

The conductors of house circuits ordinarily are intended to carry continuously not more than a moderate current, say l amperes, without becoming dangerously overheated. When a fuse on such a circuit blows and the householder does not have a l5 ampere fuse handy he frequently attempts to restore service to the circuit by inserting a larger lcapacity fuse, such as a 30 ampere fuse, in the circuit, or by bridging the plug-engaging terminals of the fuse receptacle or socket by a metal conductor. Either method of restoring service to the circuit results in an unprotected circuit. While the heavier fuse will blow when traversed by a current in excess of its rated capacity it will not protect the circuit against the effects of long continued currents that overload the circuit but not the heavy iuse. The use of a metal conductor for bridging the terminals of the fuse receptacle obviously fails to provide the circuit with protection of any kind and is in itself a source of potential danger because of the likelihood oi insecure connections between the terminals of the receptacle. The usual method of bridging the terminals of the fuse receptacle with metal is to stuff the receptacle with tinfoil, to place flexible wires in the receptacle, or a coin, and to hold the bridging material in place by screwing down upon it the blown plug fuse.

Hence an object of the present invention is the provison of a plug type fuse and its socket or receptacle, so arranged that a plug fuse having a larger current carrying capacity than is intended for the circuit cannot be inserted in the receptacle to establish circuit connections therewith and also to provide a plug fuse and a socket therefor that cannot readily be tampered with to bridge the plug-engaging circuit terminals of the socket by any means other than a plug fuse designed to be associated with the socket.

While non-interchangeable plug fuse constructions have been proposed heretofore and while nonstamperable fuse plug constructions have also been proposed heretofore there has been hereto- `fore no plugfuse having the combined properties of non-interchangeability and non-tamperability that has been satisfactory and could not be exchanged by another plug of larger capacity or bridged relatively readily by a householder; and it is an object of the present invention to provide a construction wherein the plug fuse is both non-interchangeable and substantially tamperproof.

A further object of the invention is the combination of a plug fuse and an adapter therefor, which adapter is arranged to be irremovably positioned in the ordinary plug fuse receptacle to condition the receptacle to receive only a plug ysuited to it. The adapter and the plug fuse are each provided with spaced projecting parts, the projecting parts of the adapter and fuse plug interiitting and those of the plug adapted to move relatively to those of the adapter in the act of screwing the plug into the adapter so as to catch and shear off or dislodge metal objects that may be placed in a socket for bridging the plug-engaging terminals thereof. The adapter is also provided with a movable center contact member and the plug with a corresponding center contact member, the plug contact member being so small in area of contact surface that a metal object intended to be clamped between it and the movable contact member of the adapter is dislodged by the moving projecting parts of the plug when the plug is screwed into the socket and hence is moved out of engagement with the contact members. Such an arrangement also constitutes a further object of the invention.

A yet further object of the invention is a series of plug fuses of the type immediately above described wherein for a certain low range of current carrying capacities the center contact member of the plug is within a predetermined small diameter and for larger current carrying capacities the center contact member is a larger diameter that is greater than that which will effectively engage with the movable center contact member of the adapter and enter the contact passage thereof for the purpose of moving the center contact member into engagement with the center contact of the receptacle. Thus a plug fuse above a certain capacity cannot establish circuit connections through an adapter intended for use with a plug fuse of a smaller current carrying capacity. Such a construction is a further object of the present invention.

A yet further object is generally to improve the construction of plug type fuses.

Fig. l is a sectional elevation of a fuse plug embodying the present invention inserted in a fuse receptacle. Y

Fig. 2 is a side elevation of the fuse plug, the screw-threaded shell of the plug being partly broken away and the cover being removed.

Fig. 3 is Va view of the inner or bottom end of the plug of Fig. 2, the bottom flange of the screwthreaded shell being partly broken away.

Fig. 4 is a view of the top of the plug of Fig. 2, the cover being removed.

Fig. 5 is a side elevation of the adapter of Fig.

Fig. 6 is a top View of the adapter.

Fig. '7 is a bottom view of the adapter.

Fig. 8 is a fragmentary view similar to Fig. 1 but illustrating the manner in which a fuse plug of a larger capacity is prevented from moving the center contact of the adapter into engagement with a center contact of the fuse receptacle.Y

The socket or receptacle intended to receive the plug fuse and adapter embodying the present invention comprises a suitable base lli having an upstanding annular wall l2 bounding a cylindrical space that is open at the top and in which an internally screw-threaded metal shell VI4 is located. Said shell constitutes the outer plugengaging terminal contact of the receptacle and is electrically connected with a conductor E6 to which one of the conductors of the circuit to be protected by the fuse is adapted to be secured. At the bottom of the cylindrical recess the base carries a center Contact i8 which constitutes the center terminal contact of the receptacle and is connected to a conductor 2t to which a conductor 'of the circuit to be protected is adapted to be secured.

The adapter comprising a part of the present invention includes a disc or body 22 composed of suitable insulating material and formed or provided with external screw-threads Z4 which t the internal screw threads of the terminal shell i4 and in which shell the disc is screwed to a position at the bottom of the shell where it overlies and preferably rests upon the top face of the center contact or upon some other part of the receptacle. With one or more locking members which, as here shown, comprise small diameter springy wire sections 26 which are inserted into the screwvthreaded periphery of the disc and project at an angle therebeyond and are arranged to ex to permit the disc to be screwed into the receptacle but to dig into the metal shell and lock the disc against unauthorized removal.

The disc is provided with an axially disposed cylindrical center post 28 that upstands from the upper face of the disc. The disc on the same face thereof is also provided With an upstanding annular rib 30 which is concentric with the post 28 and is radially spaced therefrom to provide an annular channel 32 between it and the post and is also spaced inwardly of the screw-threaded periphery of the disc so that there is an annular channel 34 between it and the screw-threaded shell i4 of the receptacle. The top ofk the post and the rib lie in approximately the same plane. The top of the rib is serrated or is provided with an annular series of angularly spaced and relatively axially deep notches 36 which extend through the inner-and outer faces of the rib and are preferably generally rectangular in shape, thereby providing the rib with an angular series of angularly spaced upstanding projections 38 between the notches.

The adapter and the post 28 are provided with The adapter disc l22 is provided an axially located cylindrical passage 4l! which is traversed at the top by the wall 42 of the post and at the bottom by a disc 44. Said disc is pressed into a circular recess formed in the bottom face of the adapter disc 22 co-axially with the passage 4G.

The adapter is provided with a movable center contact member .45 which comprises a cylindrical rod disposed in said passage and so guided for movement axially of the adapter that its lower end can be moved along an opening 48 in the disc 44 and into contact with the top face ofthe center contact of the receptacle. The contact member is biased for upward movement away from engagement with the center contact I8 by a .helical compression spring 5d that encircles the contact member and bears with its lower end against the inner face of the disc 44 and with its upper end against an enlarged head or flange 52 of the contact member. When no displacing pressure is exerted on the Contact member `the spring 5B holds the head 52 normally against the upper end of the passage 4B and in contact with the inner face of the wall 42. The contact member is provided with a coaxial stem .54V which is located in and is movable axially of a cylindrical passage 56 through thewall 42, the arrangement being such that when the end of the stem 54 is engaged by the center contact of a plug fuse having a center Contact that can enter the passage 5B the movable contact member can be moved downwardly to engage the center contact of the fuse receptacle.

The fuse plug also forming a part of the present invention and cooperating with the above described adapter comprises a cylindrical body 58 of suitable insulating material having a bottom wall Gil and a fuse chamber 62 above the bottom wall. The chamber can be closed in any suitable manner and the means Vherein shown comprises a transparent mica disc 64 which overlies the open end of the fuse chamber and is seated upon the top of the plug body and is retained in place by an annular metal ring 65 having a radial ange B8 that overlies the mica disc.

The plug body 58 is provided with an integral external screw thread 10 on which an internally and externally screw-threaded metal shell 12 is screw-threaded, said shell being adapted to be screw-threaded into the terminal shell i4 of the receptacle. A fuse link 14 of any suitable construction has one end thereof electrically connected to the inner face of said shell 'l2 by a mass of solder 7B which also serves to key theV shell to the plug body against rotation thereon. The other end of the fusible link is soldered or otherwise electrically connected to a center contact member 18 which is secured in the bottom wall 60 of the plug body. Said center contact member is provided with a downwardly projecting stem 80 that is adapted to engage the stem 54 of the movable contact member of the adapter and enter the passage 56 in which said stem 54 is located and -move the movable contact member downwardly into engagement with the center contact of the fuse receptacle, as the plug is screwed home in the receptacle, thereby to complete the circuit through the terminals of the receptacle.

In accordance with this invention the stem 89 is especially small in surface area and the stem of the movable contact member of the adapter is correspondingly small for a purpose hereinafter to be explained.

The bottom wall 60 is formed or provided with electrically connect the terminal shell an axially disposed recess 82 which extends inwardly from the bottom end of the plug body and in which the stem 80 of the center contact member and the upstanding post or boss 42 of the adapter plug are located. The bottom Wall 60 is also provided with a deep annular groove or channel 84 which extends inwardly from the bottom of the plug and is disposed midway between the recess 32 and the side wall of the plug, thereby providing the plug at the bottom with inner and outer concentric depending annular ribs 86 and 88 respectively. 'Ihe outer periphery of said rib 88 is engaged with a part of the screwthreaded shell 72 and said shell has an inwardly directed bottom flange 90 which underlies the bottom face of said rib 88. The rib 86 is formed or provided with a series of angularly spaced and preferably axially deep slots 92 in its bottom face and preferably are formed with straight side Walls. Said notches thereby provide the rib with an annular series of angularly spaced projections 94 which are located between the notches. The outer rib 88 is similarly formed with similar notches 96 and projections 98 which underlie the bottom iiange 90 of the screw shell 12, the notches 95 incidentally being desirable for the formation of the notches 92 and are aligned therewith. When the plug fuse is in the circuit controlling position within the receptacle the ribs 88 and 85 of the plug body are alternated with the rib and post of the adapter, the parts having substantial radial spacing therebetween and the tops of the ribs being close to or substantially seating upon the bottom of the recesses in which they are located when the plug is in circuit controlling position.

'I'he plug as thus constructed is for all general purposes non-tamperable in that theterminals of the receptacle cannot be bridged readily by a metal conductor and held in place suiciently securely to carry current. The movable center contact of the adapter prevents the circuit from being closed by the use of a metal coin disposed on top of the adapter since, while the coin may I4 and the stem 54 of the movable contact member the movable contact member cannot be moved downwardly into engagement with the center Contact I8 of the receptacle. The succesful use of tinfoil as a bridging member is also prevented. While tinfoil can be stuffed into the receptacle and connect the terminal shell I4 and the movable center contact member cf the adapter it cannot move an-d hold the center contact member into engagement with the center contact of the receptacle. If a fuse plu-g constructed as herein described, but having a blown fusible element, is screwed down upon the tinfoil the small stem 89 of the center contact member of the plug body perforates the tinfoil and thus prevents it from maintaining good contact with the center contact members and the cooperating intermeshed ribs force the tinfoil downwardly and pull it away from both the center contact members and the terminal shell. The projections on the ribs also engage the tinfoil and tear it apart on the rotation of the plug body, thereby breaking the electrical continuity of the tinfoil. If it is attempted to bridge the terminals by the use of fine ilexible wires, such as the wire conductors constituting the conductor of a iiexible electric light cord, for instance, the wires are caught by the projections of the intermeshed ribs and are moved away from circuit bridging position by the rotating plug. The stems 88 and 54 of the cooperating center contacts are so small in contact area that the act of screwing the plug body home dislodges the wires from position between the stems and hence breaks the circuit through the unauthorized bridging member.

Itis intended that the fuse body constructedv as herein described shall be provided with fusible elements which are restricted to not more than a predetermined current carrying capacity, say l5 amperes. For currents above 15 amperes a slightly modined construction will be employed. This modiiied construction is illustrated in Fig. 8. The diierence between this construction and that illustrated in Fig. l resides in the cross-sectional area of the contact stem 88a of the plug body. The stem Sila is larger in diameter than the stem 8E! and hence will overlie the stem 54 of the adapter and engage the top wall 42 of the adapter post and hence be prevented from entering the passage in the post wall and moving the movable contact member into engagement with the center contact member of the receptacle. It is intended to associate the plug body of Fig. 8 with an adapter having a stem of such size as to permit the stem 88a to operate the movable contact member of the adapter in a manner obvious without the necessity for illustration.

The plug of Fig. l cannot be removed and replaced successfully by the ordinary type of plug fuse since the center is so broad that it cannot enter the passage 56 of the adapter post to engage and depress the movable contact member into a circuit closed position.

I claim:

i. An adapter for plug fuse receptacles having center and screw shell contacts, said adapter comprising an insulating base having means providing screw-threads adapted for engagement with said screw shell and to overlie the center contact member of the receptacle, and an annular series of angularly spaced projections within the line of said screw threads.

2. An adapter ior plug fuse receptacles having center and screw shell contacts, said adapter comprising an insulating base having means providing screw-threads adapted for engagement with saidscrew shell, a center contact member, and an annular series oi' angularly spaced upstanding projections surrounding said center contact member.

3. An adapter for plug fuse receptacles having center screw shell contacts, said adapter comprising an insulating base having means providing screw-threads adapted for engagement with said screw shell, an upstanding center post, a center Contact member disposed within said center post and movable into and out of engagement with the center contact of the receptacle, and an annular series of angular-ly spaced upstanding projections surrounding and spaced from said center post.

4. An adapter for plug fuse receptacles having center and screw shell contacts, said adapter comprising a screw-threaded body adapted for engagement with said screw shell, said body having a center contact member passage therein, and means providing said adapter with an annular series of angularly spaced indentations and upstanding projections between the in'dentations about said passage.

5. An adapter for plug fuse receptacles having center and screw shell contacts, said adapter comprising a screw-threaded body adapted for engagement with said screw shell, said body having contact of Such plug fuse a center contact member, and an upstanding an-` upper face having an upstanding center post and. an upstanding serrated annular rib surrounding Y and spaced from said center post, a plate located within a recess in the lower iace of said body, said body having a passage extended axially therein and in said center post above said plate, said plate and the wall of said passage overlying said center post having co-axial openings therethrough, a contact member located in said passage having end portions movable lengthwise of said openings, and spring means biasing said contact member for axial movement. Y

V'7. A plug fuse comprising a body having a center contact and a terminal shell, fusible means connecting said contact and shell, said body having an annular series of angularly spaced outstanding projections -surrounding said center contact.

8. A plug fuse comprisingV a body having a center contact and a terminal shell, said body7 having an outstanding annular rib surrounding said center contact, said rib having notches in its end face providing an annular series of angularly spaced outstanding projections between the notches, said rib being axially longer than said notches.

9. A plug fuse comprising a body having a terminal shell and a center contact member, said body also having a bottom wall provided with radially spaced inner and outer outstanding annular ribs, the inner rib surrounding and being .spaced radially from said center contact member Vand having a series'of angularly spaced notches in its end face.

l0. A plug iusecomprising a body having a terminal shell and a center contact member, said body also having a bottom wall provided with radially spaced inner and outer outstanding annular ribs, the inner rib surrounding said center contact member and having a series oi angularly spaced notches in its end face, said outer rib Yalso having a similar series oi' notches that are radially aligned with the notches of said inner rib.

11. A plug fuse comprising a body having a terminal shell and a center contact member, said Vbody also having a bottom wall provided with radially spaced inner and outer outstanding annular ribs, the inner rib surrounding and being spaced radially from said center contact member and having a series oi angularly spaced notches in its end face, said'outer rib also having a similar series of notches that are radially aligned with the notches of said inner rib, and said terminal shell having an end flange which overlies and is seated upon the end face of said outer rib.

12. A plug fuse comprising a body having a terminal shelland a center contact member, said body also having a bottom wall provided with radially spaced inner and outer outstanding annular ribs, the inner rib surrounding and being spaced radially from said center contact memradially spaced innerV and outer outstanding annular straight-sided ribs, the inner rib surrounding and being spaced radially from said center contact member and havingV a series of angularly spaced notches in its end face, and said center contact member being located in the bottom of the recess within said inner rib.

14. In a plug fuse having contacts and means providing4 it with a screw-threaded engagement with its socket, the combination therewith of an externally-disposed, tamper-preventing, socketentering tooth on said plug.

15. In a plug fuse having contacts and'adapted to be rotated into a.socketrhaving cooperating contacts, the combination therewith of a tamperpreventing tooth on the plug between its contacts and eccentric of the plug axis.

16. The combinationrwith a plug fuse and a socket in which the plug is rotatable and both having cooperating contacts, of cooperating shear-members of the plug and socket shearing by relative rotation therebetween.

17. The combination of a plug fuse and a socket therefor having cooperating contact terminals, means providing a screw-threaded connection between the plug and socket, said plug and socket each having an annular projecting rib provided with angularly spaced notches in the end face thereof, said ribs being positioned one Within the other when the plug is within the socket and with the open ends of the notches facing in opposite directions, said ribs being located between the contact terminals of said socket.

18. The combination of aplug fuse having a center contact and a screw-threaded terminal shell, a socket having a center contact, and a screw-threaded terminal shell cooperating with the terminal shell of said plug, said socket having an upstanding center contact carrying center post and an annular series of angularly spaced upstanding projections surrounding and radially spaced from said center post, and said plug having an annular series of angularly spaced outstanding projections surrounding the center contact of said plug and positioned for location between said post and said annular series of projections of said socket.

19. The combination of a plug fuse and a socket therefor, said plug fuse having a center contact and a screw-threaded terminal shell, and a projecting annular rib surrounding and spaced from said center contact and provided with a series of angularly spaced notches` in its end face, and said socket having a center Contact and a screwthreaded terminal shell cooperating with the center contact and shell of Vsaid plug and also having an upstanding center post located within said rib oi" said plug when the plug is within its socket, said socket also having an annular upstanding rib having a series ci angularly spaced notches in its end face, said last named ribV surrounding the rib of said plug.

2i). The combination of a plug fuse and a socket therefor, said plug fuse having a bottom wall and center and screw shell contacts, said bottom wall having outer and inner radially-spacedannular ribs the inner rib of which encloses an axial recess in which said center contact is located, said outer body having a rib constituting in part a. support for said screw shell, and said socket having a center contact and screw shell cooperating with said center oontact and shell of said plug, said socket also having an axially disposed upstanding center post adapted to receive said center contact of said plug and to be received within the axial recess or" said plug, and an annular upstanding rib adapted to be received in the recess between the annular ribs of said plug.

21. The combination of a plug fuse and an adapter arranged for insertion in a socket having center and screw shell contacts, said adapter comprising an insulating screw-threaded body adapted for engagement with the screw shell of said socket above the center contact thereof, said adapter body having an annular series of angularly spaced upstanding projections, said plug comprising a body having a center contact member and a screw-threaded terminal adapted for electrical connection with the screw shell of said socket, said plug body having an annular series of angularly spaced projections which surround the center Contact member of said plug body and radially confront the projections of said adapter.

ELMER H. TAYLOR. 

